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Calcium

Calcium is a member of the alkaline-earth family of metals with the atomic symbol Ca, atomic number 20, and atomic weight 40. It is a soft, silvery-white metal that does not occur naturally in its pure form. It occurs abundantly as limestone (CaCO3), gypsum (CaSO4 · 2H2O), and fluorite (CaF2). It is the fifth most abundant element in the Earth's crust, and its compounds are among the most important substances on Earth. It is an essential constituent of leaves, bones, teeth, and shells.

Calcium readily forms a white coating of oxide in air, reaacts with water, burns with a yellow-red flame, forming the oxide. The metal is used as a reducing agent in preparing other metals such as thorium, uranium, zirconium, etc.

Natural calcium contains six isotopes; sixteen other radioactive isotopes are known.

Important Calcium Compounds

  • calcium carbide (CaC2) - used for generating acetylene gas
  • calcium chloride (CaCl2) - used as drying and dehydrating agent; electrolyte repplacement
  • calcium cyanamide (CaCN2) - fertilizer
  • calcium hypochlorite (Ca(OCl)2)- water treatment and bleaching agent
  • calcium nitrate (Ca(NO3)2) - component of fertilizers, explosives, matches
  • calcium sulfide (CaS) - lubricant additive; component of luminous paints

Most calcium compounds are white solids, used to be called limes, but now "lime" technically refers only to calcium oxide (CaO). The Greeks called this substance (and rocks in general) "calx" and this is where the word "calcium" came from. The ancient Romans and Greeks used lime to create mortar, a soft mixture of lime with water and sand that hardens as it dries. It is still used to hold stones and bricks together 1.

By adding water to lime, the Romans created calcium hydroxide (Ca(OH)2), commonly called slaked limeor hydrated lime. It is used as a fertilizer, a sewage treatment chemical, and an ingredient in mortars and plasters.

Though lime was prepared by the Romans in the first century under the name calx, the metal was not discovered until 1808 by Sir Humphry Davy (1778-1829), a British chemist.

Essential Element of Life

Without calcium, life would be impossible because it is essential for the growth of both plants and animals. The divalent cation, or ionized, calcium (Ca2+)is a mineral that is critical to normal human health, playing vital roles in the structure of the bony skeleton, cellular communication, fertilization, metabolism, blood clotting (as factor IV), nerve impulse conduction, and muscle contraction.

Ninety-nine percent of the body's calcium is in the bones and teeth where it plays two roles. First, it is an integral part of the bone structure. Second, it serves as calcium bank, offering a readily available source of the mineral to the body fluids should a drop in blood calcium occur 2.

A number of calcium properties make it a highly suitable intracellular messenger. Calcium is much more suitable as a signaling ion than other prevailing ionic species because of the size of its ionic radius, which is smaller of the potassium ions (K+) and Chloride ions (Cl-) and small enough to fit into intracellular pores. The other factor is that it can bind tightly to proteins. The capacity of Ca to be coordinated to multiple ligands-from six to eight oxygen atoms-enables it to cross-link different segments of a protein and induce significant conformational changes 3,4.

Diseases Associated with Impaired Calcium Metabolism

Many different metabolic disorders affect calcium metabolism (absorption, transport, storage, and utilization) and can lead to abnormally high or low levels of calcium in the blood. These include:

  • Calcinosis - deposition of calcium salts in tissues
    • Calciphylaxis - induced systemic hypersensitivity in which tissues respond to appropriate challenging agents with a sudden local calcification.
    • CREST Syndrome - an acronym for Calcinosis, Raynaud phenomenon, Esophageal dysfunction, Sclerodactyly, Telangiectasis; a mild form of limited scleroderma, a multi-system disorder.
    • Nephrocalcinosis - Calcification of the renal tissue itself.
    • Vascular Calcification - Deposition of calcium into the blood vessel structures. Excessive calcification of the vessels are associated with atherosclerotic plaques formation particularly after myocaridal infarction.
  • Pathologic Decalcification - loss of calcium salts from bones and teeth. Bacteria may be responsible for this occurrence in teeth. Old age may be a factor contributing to calcium loss, as is the presence of diseases such as rheumatoid arthritis.
  • Hypercalcemia - abnormally high level of calcium in the blood
  • Hypocalcemia - low blood calcium levels
  • Osteomalacia - a condition marked by softening of the bones due to impaired mineralization
  • Pseudohypoparathyroidism - hereditary condition caused by failure of response to parathyroid hormones; characterized by hypocalcemia and hyperphosphatemia
  • Rickets - condition caused by deficiency of vitamin D

In dogs, the most common disorder of calcium metabolism is puerperal hypocalcemia, also called postpartum hypocalcemia, periparturient hypocalcemia, puerperal tetany, and eclampsia.

References

  1. Greg Roza. Calcium
  2. Ellie Whitney, Eleanor Noss Whitney, Sharon Rady Rolfes. Understanding Nutrition
  3. Calcium Ion Is a Ubiquitous Cytosolic Messenger
  4. Connie Weaver, Robert Proulx Heaney. Calcium In Human Health
  5. CRC Handbook of Chemistry and Physics, 90th Edition (2009-2010)
  6. Medical Subject Headings

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